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C:B ratio

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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C:B ratio

Unread postAuthor: stevenarroyo » Tue Sep 23, 2008 7:00 pm

am planing on making a new Combustion Cannon with all the good stiff propane metering/ camber fan. the cannon is going to be a over/under design.

my question is i have a C:B ratio of 1.22:1 is that good??
i did not add the 2 elbows that are 1 1/2in size.

so if some1 can help me?!?!

i was never good with math... lol
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Re: C:B ratio

Unread postAuthor: brogdenlaxmiddie » Tue Sep 23, 2008 7:22 pm

stevenarroyo wrote:i was never good with math... lol

Apparently you weren't pretty good with grammar either! :roll:

EDIT- Also, why is this in the showcase section :?: :shock:
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Unread postAuthor: stevenarroyo » Tue Sep 23, 2008 7:28 pm

that too

and i would like for people to help me not make fun of me.
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Unread postAuthor: brogdenlaxmiddie » Tue Sep 23, 2008 7:30 pm

Fair enough, I think that your C:B is pretty good, but I think that an important thing would be the space inside of the elbows. I'm not an expert on the whole C:B thing but I personally try to go for almost a 2:1 just because I don't look for performance in my combustions, but noise :D
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Unread postAuthor: stevenarroyo » Tue Sep 23, 2008 7:32 pm

i hear that a good C:B is around 1.6 or 1.5 i think?
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Unread postAuthor: brogdenlaxmiddie » Tue Sep 23, 2008 7:33 pm

It very possibly is, but are you going for sound, or performance?
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Unread postAuthor: stevenarroyo » Tue Sep 23, 2008 7:35 pm

i want to get more performance then sound

sound would not hurt too lol
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Unread postAuthor: mark.f » Tue Sep 23, 2008 8:23 pm

If you're using metered propane and a chamber fan, then a CB ratio of about 0.8:1 is desired. Are you holding your chamber size or barrel size constant in your design, though?
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Unread postAuthor: stevenarroyo » Wed Sep 24, 2008 11:33 am

my chamber volume is 87.21 cu in without the (2) 1 1/2inch elbows

and my barrel volume is 71.44 cu in

my chamber size is 3" x 12" long
and barrel is 1 1/2" x 36" long
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Unread postAuthor: jimmy101 » Wed Sep 24, 2008 2:05 pm

1. Read the Wiki page on CB ratio.

2. Get a copy of HGDT (search for it in the Wiki). It'll answer your questions about how changing the CB affects the gun's performance. The difference in performance between CB 0.8 and 1.2 isn't going to be huge, something like 10-20% in muzzle velocity (20-30% in kinetic energy).
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Unread postAuthor: stevenarroyo » Wed Sep 24, 2008 3:51 pm

ok thanks :D :D :D :D
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Unread postAuthor: nickz » Thu Sep 25, 2008 6:18 am

My current gun has a 8.something to one ratio, it is a 30" by 1 1/2" chamber with a 24" by 1/2" barrel because that all I had laying around.And it shoots very good. According to EVBEC I would need a 158" by 1/2" barrel to make 1.2 to 1, and it would almost double the velocity.

I would need an 20 foot barrel to get .8 to 1, and it would shoot at over 560 fps.
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Unread postAuthor: Hotwired » Thu Sep 25, 2008 8:53 am

Possibly.

Or then again such a long barrel could give the gases behind the projectile time to cool enough to cause a vacuum and make the projectile lose energy/not exit at all.
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